After doing rpi-update on kernel 4.19.115-v7+ on ubuntu-mate 16.04.2 the raspberry pi 3 are unable to reboot and boot up at all. My HDMI display give No Signal. It have been having rebooting problems since the rpi-update kernel 4.19.115+. Ubuntu-mate 16.04.2 are brick or broken and not working.

I check my raspberry pi 3, there is no problem running with another SD Card on Raspbian.

Now I cannot boot up my ubuntu-mate 16.04.2 at all. All my files and bootmarks are stuck in there and there is no way to backup.

When I inserted the ubuntu-mate 16.04.2 on an external SD Card reader dongle, i can only see PI_ROOT and PI_BOOT.

I really do not know how to recover my ubuntu-mate 16.04.2 to make it boot.

I even try using another SD Card with fresh install ubuntu-mate 16.04.2 and do a rpi-update to the latest kernel 4.19.115-v7+. After upgrading, it cannot reboot and HDMI gives no Signal. So both my older SD Card and the Newer SD Card cannot boot at all.

Now your Pi will boot from third previous kernel version (the first is 0), depending of kernel upgrades your system saved since last time you autoremoved packages.
After this, you can remove newer headers and image kernels and return GRUB_DEFAULT=0, but this is another history.

Tim does it work at your raspberry pi 3???
I try many times still the same thing. Sometimes it cannot reboot and keeps having HDMI No Signal.

I have revert back to the older rpi-update kernel.
It got to do with Ubuntu-Mate 16.04.02 Operating System issues. I did not have any problems updating to the latest rpi-kernel with Raspbian. Only problems with Ubuntu-Mate 16.04.2